[IPV4] bug: broken open-coded inet_make_mask() (multipath_wrandom)

multipath_wrandom.c::__multipath_lookup_weight() contains open-coded
attempt at inet_make_mask(); broken on big-endian.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>